Introduction to Titration
Revisit delivered volume, reacting proportions and endpoint bias before reading a pH titration curve.
AP Chemistry Topic 4.6 · CED printed p. 83 / PDF p. 90. This teaching, practice and feedback were added for the AP edition; original author material remains separately traceable.
Before you start
- Moles and molarity
- Ionic charges and molecular formulas
- Intermolecular versus intramolecular interactions
- Ideal gas equation with kelvin temperature
A titration counts an unknown analyte by reacting it with a measured amount of known titrant. The reaction must be specific, fast enough, and sufficiently complete for stoichiometry to apply. At equivalence, exactly the required reacting amount of titrant has been supplied; that does not require equal volumes or equal moles when coefficients differ. The endpoint is the observed change used to locate equivalence, such as an indicator color or a measured property change. It can occur slightly before or after true equivalence. Read a buret by subtracting initial from final reading, not by using the final reading alone. On a property-versus-titrant-volume graph, use labeled volume units and a sensible scale. Infer equivalence from stoichiometry or the transition feature supplied by the measurement; an acid–base equivalence point is not automatically pH 7. Replicate readings reveal precision, while a consistent endpoint overshoot biases every result.
Let's work through it
A 20.00 mL H2SO4 sample requires 24.60 mL of 0.1000 M NaOH for complete neutralization of both acidic protons.
- H2SO4 + 2OH− → SO42− + 2H2O. The equivalence ratio is 1 mol acid to 2 mol hydroxide.
- n(OH−) =0.02460 ×0.1000 =0.002460 mol; n(acid) =0.001230 mol.
- M(acid) =0.001230/0.02000 =0.06150 M. A late endpoint would make the inferred acid concentration too high because it records excess base as if it reacted with acid.
Try it from memory
Pause & retrieve
Try it before you peek.
Write your answer and the reason from memory. Then compare with the worked answer. Your self-assessment is a study decision, not an automatically graded score.
Question 1
Are endpoint and equivalence point identical by definition?
See every recall question with its answer
These references preserve each prompt and its answer for direct evidence links. Try the interactive questions above before opening the worked reasoning.
Retrieval 1
Are endpoint and equivalence point identical by definition?
Worked answer and reason
No. Equivalence is the stoichiometric condition; endpoint is the measured signal used to estimate it.
An observation is an estimate of a chemical condition.
Retrieval 2
At equivalence for H2A + 2OH−, what amount ratio is needed?
Worked answer and reason
Two moles of hydroxide per mole of acid. Equal titrant/analyte moles would neutralize only half the required protons in this model.
Balanced coefficients set equivalence.
Catch the tempting mistake
- Equivalence requires equal volumes.
- Concentrations and coefficients determine the volume ratio.
- Any neutralization equivalence is at pH 7.
- The product species can react with water; pH depends on acid/base strength. Stoichiometric equivalence is the unit’s criterion.
Put it to work
Give the chemical reason as well as the calculation. Worked solutions are on a separate page.
- Unit 4 problem 11 · ap application · data
- Unit 4 problem 12 · ap synthesis · verbal
Scientific calculator workspace
Use this workspace for arithmetic, logarithms and elementary functions. Keep intermediate precision and report final values with appropriate units and significant figures. Graphing and general equation solving need a suitable approved tool.
Scientific calculator
This calculator requires JavaScript. Use the physics formula sheets and show your working manually.
+ − * / ^ ! · pi · e · sqrt · sin, cos, tan · asin, acos, atan · atan2(y,x) · ln, log · abs · exp · hypot(x,y). Use * between factors. Keep units in your written working.
For the teacher
- Ask students to sketch the observable versus volume and label the inferred equivalence.
- Use a consistent buret error to separate precision from accuracy.
Source objectives and scope
Source edition: ap-chemistry-ced-fall2024-local-b5dfe867. See this topic in the course outline →
- 4.6.A
- Identify the equivalence point in a titration based on the amounts of the titrant and analyte, assuming the titration reaction goes to completion.
- 4.6.A.1
- Titrations may be used to determine the amount of an analyte in solution. The titrant has a known concentration of a species that reacts specifically and quantitatively with the analyte. The equivalence point of the titration occurs when the analyte is totally consumed by the reacting species in the titrant. The equivalence point is often indicated by a change in a property (such as color) that occurs when the equivalence point is reached. This observable event is called the endpoint of the titration.
Science references for this teaching
- College Board AP Chemistry Course and Exam Description, Fall 2024 — Exact unit learning requirements and exclusions; supplied PDF is pinned by the integration catalog.
- OpenStax Chemistry 2e: Reaction Stoichiometry — Scientific check: mole ratios and limiting reactants; all numerical tasks are newly authored.
- OpenStax Chemistry 2e: Quantitative Chemical Analysis — Scientific check: equivalence versus observable endpoint, stoichiometric analysis.
Glossary and deeper reading · 6 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
-
Mole
A mole is an amount of substance containing exactly 6.02214076 × 10²³ specified entities. The entities can be atoms, molecules, ions, or formula units, so the counted entity must be named. For example, one mole of oxygen molecules contains two moles of oxygen atoms.
-
Molarity
Molarity is the amount of a solute in moles divided by the final solution volume in liters. It describes concentration rather than the total amount of solute. For example, 0.10 mole dissolved to make 0.50 liter of solution gives a molarity of 0.20 mole per liter.
-
Molecular formula
A molecular formula gives the actual number of each kind of atom in a molecule. It can be a whole-number multiple of the empirical formula. For example, glucose has molecular formula C₆H₁₂O₆ and empirical formula CH₂O.
-
Ideal gas law
The ideal gas law relates pressure, volume, amount, and absolute temperature in an idealized gas model. It treats particles as having negligible volume and no intermolecular attractions. For example, at fixed amount and temperature, doubling the container volume halves the ideal gas pressure.
-
Titration
Titration measures an analyte by its reaction with a measured amount of another reagent. The balanced reaction and the observed endpoint must be connected to the equivalence condition. For example, an acid's amount can be inferred from a measured volume of a base with known concentration.
-
Analyte
An analyte is the substance being identified or measured in an analysis. Its amount or concentration is the target of the measurement rather than necessarily the largest component of the sample. For example, an unknown acid is the analyte in an acid–base titration.